Transverse flux electrical machines include a circular stator and a circular rotor, which are separated by an air space called air gap, that allows a free rotation of the rotor with respect to the stator, and wherein the stator comprises soft iron cores, that direct the magnetic flux in a direction that is mainly perpendicular to the direction of rotation of the rotor. The stator of transverse flux electrical machines also comprises electrical conductors, defining a toroid, that is coiled in a direction that is parallel to the direction of rotation of the machine. In this type of machine, the rotor comprises a plurality of identical permanent magnet parts, that are disposed so as to create an alternated magnetic flux in the direction of the air gap. This magnetic flux goes through the air gap with a radial orientation and penetrates the soft iron cores of the stator, which directs this magnetic flux around the electrical conductors.
In the transverse flux electrical machine of the type comprising a rotor, which is made of a plurality of identical permanent magnet parts, and of magnetic flux concentrators, the permanent magnets are oriented in such a manner that their magnetization direction is parallel to the direction of rotation of the rotor. Magnetic flux concentrators are inserted between the permanent magnets and redirect the magnetic flux produced by the permanent magnets, radially towards the air gap.
The transverse flux electrical machine includes a stator, which comprises horseshoe shaped soft iron cores, which are oriented in such a manner that the magnetic flux that circulates inside these cores, is directed in a direction that is mainly parallel to the direction of rotation of the rotor.
The perpendicular orientation of the magnetic flux in the cores of the stator, with respect to the rotation direction, gives to transverse flux electrical machines a high ratio of mechanical torque per weight unit of the electrical machine.
U.S. Pat. No. 5,051,641 describes a transverse flux electrical machine with flux concentration, in which each of the magnetic flux concentrators of the rotor must be fixed to a disc or to a common rotor ring by means of bolts and nuts. This type of machine also includes permanent magnet parts having the same radial dimension as the magnetic flux concentrators, and where each permanent magnet part must be fixed to the magnetic flux concentrators by using a glue that is applied between these two parts. The machine is also provided with a stator, that consists of a plurality of horseshoe shaped soft iron cores which are radially located on both sides of the rotor. The number of horseshoe shaped soft iron cores on the first side of the rotor is equal to the number of horseshoe shaped soft iron cores on the second side of the rotor.
U.S. Pat. No. 5,877,578 presents a transverse flux machine with flux concentration, in which the stator is located on both sides of the rotor, but where the magnets may be inserted into guides. The guides should however be fixed to a disc or a ring by using bolts, which adds to production activities.
U.S. Pat. No. 5,854,521 presents a transverse flux machine without flux concentration where the stator is located on one side only of the rotor, but where the magnets are magnetized perpendicularly to the direction of rotation of the rotor, which increases magnetic leakage fluxes between two adjacent magnets, and consequently decreases the converted power per weight unit of the machine.
The main problems of the transverse flux machine with flux concentration of the prior art are the following. Production of the rotor is difficult, because the magnetic flux concentrators must be fixed to a disc or a common rotor ring by means of bolts and nuts. The machine as a whole is not very rigid since the stator is localized on both sides of the rotor. Finally, the maximum value of the mechanical torque on the shaft of the machine per weight unit of the machine is limited by the magnetic saturation of the horseshoe shaped cores, since the distance of the air gap is the same in the aligned and unaligned position of the rotor.